Not sure about the numbers on this one, but there's the general concept.

I can't really see the unattach ability being used much here by opponents. You'd most want to do it on this thing's controller's turn, preferably during combat, but obviously that's not allowed. It looks like it's paying 3 life for something they could just spend 1 mana to undo. Now if the costs were inverted, 1 to cast and 3 to equip, it'd be more interesting.

I made it playable as an instant, but maybe that makes this suck. It would be... interesting if the equip cost was also life.

Maybe not as interesting as you may think it is. If one value is life, and the other value is life, then the end result will probably be that the creature is never equipped, or always equipped. If we assume that both players have perfect knowledge, then they would know which game state is better (everyone losing life, or no one losing life) and choosing to do that.

While some Spikes will like this, many Timmys will hate this... for the same reason. It makes your opponent and/or yourself look stupid when you are wrong.

With pay life vs. pay mana however, this isn't so cut and dried. You'll always need to pay mana of differing amounts, so the decision to equip or unequip is more complex. And that complexity makes Spike happy anyways...

Design philosophy aside, I like this card and I like what it's doing. You should expect people to complain about this design because other people will probably like it, and want it to fit their expectations. In other words, their complaining because they like it... good news.

If I was to change anything about this card as it stands, I'd get rid of the -1 to toughness. I know it's probably there to support the flavor, but I personally don't think it makes the card more compelling... just more confusing.

Would it help to make the unequip not during combat, or perhaps, make it an "equip unless an opponent pays 3 life", then you can have your bidding war in your main phase before combat, but your opponent can't always trump it by unequipping at instant speed during combat?

OTOH, maybe cheaping the price and letting them unequip during combat is more interesting after all: it can only happen once a turn, and you can't attack with impunity, but also, the ability causes you to chip away at them three life at a time, that's probably still quite nice.

Alternatively, you could combine the last and first ability: make it "+3/+0. Equip 2. Pay 3 life: Equipped creature gets -0/-1. Only any opponent may play this ability" :)